No clinically significant changes in pulmonary function following stereotactic body radiation therapy for early- stage peripheral non-small cell lung cancer: an analysis of RTOG 0236

Abstract

Purpose: To investigate pulmonary function test (PFT) results and arterial blood gas changes (complete PFT) following stereotactic body radiation therapy (SBRT) and to see whether baseline PFT correlates with lung toxicity and overall survival in medically inoperable patients receiving SBRT for early stage, peripheral, non-small cell lung cancer (NSCLC).

Methods and materials: During the 2-year follow-up, PFT data were collected for patients with T1-T2N0M0 peripheral NSCLC who received effectively 18 Gy × 3 in a phase 2 North American multicenter study (Radiation Therapy Oncology Group [RTOG] protocol 0236). Pulmonary toxicity was graded by using the RTOG SBRT pulmonary toxicity scale. Paired Wilcoxon signed rank test, logistic regression model, and Kaplan-Meier method were used for statistical analysis.

Results: At 2 years, mean percentage predicted forced expiratory volume in the first second and diffusing capacity for carbon monoxide declines were 5.8% and 6.3%, respectively, with minimal changes in arterial blood gases and no significant decline in oxygen saturation. Baseline PFT was not predictive of any pulmonary toxicity following SBRT. Whole-lung V5 (the percentage of normal lung tissue receiving 5 Gy), V10, V20, and mean dose to the whole lung were almost identical between patients who developed pneumonitis and patients who were pneumonitis-free. Poor baseline PFT did not predict decreased overall survival. Patients with poor baseline PFT as the reason for medical inoperability had higher median and overall survival rates than patients with normal baseline PFT values but with cardiac morbidity.

Conclusions: Poor baseline PFT did not appear to predict pulmonary toxicity or decreased overall survival after SBRT in this medically inoperable population. Poor baseline PFT alone should not be used to exclude patients with early stage lung cancer from treatment with SBRT.

Figure 1

Kaplan-Meier overall survival (OS) curves of patients with baseline pulmonary function test values greater and less than the mean % predicted values. A. forced vital capacity (FVC) greater (solid line) and less than (dashed line) its mean value; B. forced expiratory volume in the first second of expiration (FEV1) greater (solid line) and less than (dashed line) its mean value; C. FEV1/FVC greater (solid line) and less than (dashed line) its mean value; D. total lung capacity (TLC) greater (solid line) and less than (dashed line) its mean value; E. diffusing capacity for carbon monoxide (DLCO) greater (solid line) and less than (dashed line) its mean value; F. poor baseline pulmonary function (PF) and normal baseline PF but with other reasons for medical inoperability.